Saguaro, Opuntia and Other Cacti are Permanent Carbon Sinks

In case it wasn’t already obvious, I have deep love for trees, so I’ve planted different trees all over the place in Michigan and Tucson.

On the trees I’ve planted along the way:

Since I just moved back to Tucson, I’ve been planning to plant a tree after I settled wherever I ended up living.

So I was thinking about the tree I’d plant, thinking thinking thinking, but wavering mostly. Maybe a Palo Verde, or perhaps another Mesquite from seeds collected outside the Classics department on UofA’s campus, like the one I propagated back in 2015 just to see if I could and then planted in the yard where I was renting. (That mesquite is flourishing! I see it from the main road over the privacy fence whenever I drive by.) Or should it be a Desert Willow to match the one already in the ground in front of the place I’m renting? Or should it be a Locust? My mind tends to reel when confronted with a barrage of options, and, despite being in a “desert,” Tucson is packed with diverse flora, so there are an incredible number of choices. All of these trees are outrageously beautiful, each with a remarkable flower, so spectacle doesn’t narrow down my choices.

At a late stage in the decision-making process, having already moved into a place and after I’d given up my internet search, resigning myself instead to going into a nursery and just looking around, I realized that, obviously, what I need to plant are a couple saguaros.

But also ever since I’ve come back, actually long before that, I’ve been fixated on cacti—big cacti, lil cacti, round cacti, barrel cacti, cholla cacti, and, of course, Saguaros.

‘But…’, the thought came quick in response, ‘how good are they at sucking up carbon?!’

Garvie’s Saguaro Study

Surprise (to me)! Along with other cacti, saguaros turn captured carbon into calcium carbonate and calcite, effectively removing that carbon from the atmosphere forever.

Here’s the study: Garvie, Laurence AJ. 2003. American Mineralogist 88: 1879–1888. [The link leads to the original paper by Garvie, a geologist at the University of Arizona.]

And here’s a quicker/simpler version, reporting on Garvie’s paper:

This is game changing!

Turns out, saguaros and other cacti are special allies in the fight to clean up what industrialized human populations* have wrought. They store that carbon not in an organic material that breaks down relatively rapidly and thereby releases much of that carbon back into the atmosphere, as trees do, but actually in an inorganic mineral, calcite. Cacti turn atmospheric carbon into a mineral!!!

*. To be clear: it is not our entire species that is at fault here, but only a minority of us, those of us in the WEIRD world, who have been filling the air with combustion exhaust ever since the so-called Industrial Revolution.

I’m glad to know this, but a little surprised I hadn’t heard anyone talking about it before. Why aren’t more people talking about this?!

By the way, guess what made the water in the aquifer below Tucson so notoriously calcareous… I burned through three coffee-makers in two years the first time I was here from the calcium building up inside. These days it’s my electric kettle that collects the ‘scale’: a pure white layer like a blanket of snow. Now I know the source of all that calcium dissolved in the water underground, beneath the innumerable saguaros and other cacti that have lived and died, since the seas retreated. The source of the calcium in our water is literally carbon in the sky sucked into a cactus.

I’m going to get two saguaros to begin with, young ones, with intact tap roots (because the tap root is an individual’s anchor, keeping them upright. Without that root, an individual is at an extreme disadvantage since all other roots only go 4″ deep). I’ll plant them somewhere in this yard where I’m renting, while also trying to get my landlord to swear on whatever he cares about that he won’t harm (or outright remove) anything I plant.

Opuntia and Other Quick-Growing Cacti

For quicker carbon capture, plant opuntia, ‘prickly pear.’ As Garvie says, these grow much faster than saguaros (on which see this editorial from AZ Central by Linda Valdez), so he envisions each resident of Tucson planting a couple opuntiae to offset our emissions.

As it happens, one of my neighbors put out to the road large chunks of a prickly pear. I let them sit there for more than a week untouched before I decided they were definitely for the taking. I grabbed a bit of it last night, along with some Pencil Plant (Euphorbia tirucalli [wikipedia]).

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